The invention relates to a method for trimming print products in a trimming apparatus, the apparatus comprising at least one upper knife, one immovable lower knife, one movable press crosshead, a drive, and a control unit. Prior to the trimming operation, the print product is pressed down by the press crosshead. Following the trimming operation, the upper knife and the press crosshead are lifted up and the trimmed product is conveyed further with a conveying device. The invention furthermore relates to a trimming apparatus for realizing the above-described method.
Methods of the aforementioned type are used in particular in the print-processing industry, for example, for trimming stitched paper signatures along three open edges. The trimming apparatus is coordinated with a conveying device for conveying the print products from a first to a second trimming station. The print product is trimmed along one fore-edge in the first trimming station, in a direction transverse to the conveying direction. Following the fore-edge trimming, the print product is supplied by the conveying device to the second trimming station in which the top and bottom edges are trimmed simultaneously. The print product, which is trimmed on three sides, is then conveyed away from the trimming apparatus by the conveying device.
The two trimming stations operate simultaneously by trimming the fore-edge of a first print product and, simultaneously, trimming the top and bottom edges of a second print product. The first trimming station is provided with a movable upper knife, an immovable lower knife, and a press crosshead, also called a press guide or ruler. The second trimming station is provided with two movable upper knives, arranged at a distance to each other on the sides. An immovable lower knife and a press crosshead are assigned to each upper knife, wherein the press crosshead is connected to the upper knife. The press crosshead moves ahead of the respective knife before the start of the trimming operation, so that the print products are pressed down at the start of the trimming operation. Following the trimming operation, the press crosshead is driven to lag behind the upper knife. The print product can be conveyed further once the press crosshead, which is driven to lag behind the upper knife, is lifted off the print product.
Trimming apparatuses of this type increasingly have to meet narrower trimming tolerances with simultaneously higher production capacities. More precise and faster reacting transport and control systems are correspondingly needed for the intermittent transport and/or the movement for advancing the print products in the trimming apparatus. The presently available drive systems for advancing products, used in known methods and apparatuses, meet these requirements only up to a specific cycle number and/or production capacity.